1. Field of the Invention
This invention relates to encoding and decoding audio frequency signals on a television video signal while maintaining said video signal in a standard form, thus eliminating audio to video delay problems and providing high quality audio frequency channels.
2. Description of the Prior Art
As television technology develops, several previously unforseen audio related problems are also developing. One of these problems pertains to properly maintaining the timing or synchronization relationship of audio and video signals. This problem was explained in U.S. Pat. No. 4,313,135 which may be referred to for further details. Another problem is that normal broadcast television audio is limited to one channel of 5 KHz bandwidth. With the drastic improvements in television video equipment over the past years, the image quality of television programs now far surpasses the audio quality. There is a great need for a device which can improve the audio quality of a television program, preferably to a stereo high fidelity level, and which can encode this audio in the video signal to prevent audio to video delay problems. Such an encoded audio system will have substantial cost benefits in the transmission of television programs by eliminating the need for a separate audio channel.
Several television systems exist which add digitized audio in one form or another in the blanking interval of the television video signal. This sytem has been used as a scrambling technique where it is desirable to prevent unauthorized viewing of the television program. Digitized audio requires a great deal of bandwidth, thus causing a substantial portion of the video blanking interval to be filled with digital data seriously affecting sync and burst. Unfortunately, this digital audio in blanking is not directly compatable with existing video systems and the digital audio conversion components, i.e. A-D and D-A, are fairly expensive. The digital audio in blanking does work well as a scrambled system because the digital information requires most sync information to be removed causing television receivers to malfunction.